The description in the CPT book states "service(s) provided on an emergency basis in the office, which disrupts other scheduled office services"
Using it for 'add-on's' is not what it is meant for. You have set aside a certain number of slots for add-ons so they really shouldn't be disrupting the provider.
I don't have anything written up specifically by MD Medicare, but if you go by the description in the cpt book using it for add-ons is not appropriate.
Michele